As used herein, the term “optical cross connect” refers generally to any device that optically interconnects groupings or “nodes” of fibers with other “nodes” of fibers. The term “perfect shuffle” as used herein refers to a particular configuration of an optic cross-connect in which each output node contains a fiber from each input node. As used herein, the terms “input node” and “output node” are used for illustrative purposes to provide a distinction between the two sets of nodes. It should be understood, however, that this designation should not limit the invention to a particular direction of propagation of light through the nodes. For example, it is well recognized that an input in a cross-connect may be considered an output if the direction of propagation of light changes, thus, in practice, what is referred to, as an input node may actually be a node through which light exists.
The concept of a perfect shuffle is shown systematically in FIG. 1. As shown, input nodes 1-1 through 1-64 are interconnected with each of the output nodes 2-1 through 2-64. For simplicity, the interconnections of nodes 1-5 through 1-63 and 2-5 through 2-63 have been eliminated from the figure. Additionally, it should be understood that, in a prefect shuffle, each node would be connected to 64 other nodes as opposed to merely the five as shown in the FIG. 1. In such a design, all input nodes must be able to communicate with each output node. Thus, the number of interconnections for each node is equivalent to the number of nodes. For example, to effect the interconnection of 8 input nodes to 8 output nodes, there must be 8 interconnections per node.
The number of nodes and thus the number of interconnections therewith depend upon the particular application of the optical cross-connect. For example, applicants have identified that optical cross connects are particularly well suited for switching in dense wavelength division multiplex (DWDM) networks as found in mesh/ring long-distance networks, metro rings, and feeder rings. In such applications, a network fiber may contain many channels of optical signals with each channel propagating at a different wavelength. To effect switching, these channels must be separated or “de-multiplexed,” such that each channel propagates on a dedicated fiber. At this point, each fiber can be interconnected from one input node to each of the output nodes. The various channels contained on discrete fibers corresponding to a particular output node are then combined or “multiplexed” on to a fiber to again achieve a DWDM transmission. Aside from these DWDM applications, applicants have identified also that optical cross-connects can be used in such switching applications as routers. A schematic diagram of the various applications for optical cross connects are shown in FIG. 2.
In addition to these applications, applicants envision using an optical cross connect for interconnecting processors or other components within a computer.
Traditional approaches for interconnecting optical nodes typically involve a hybrid optoelectric configuration. More specifically, rather than interconnecting the various nodes in the optical domain, optical signals are converted to electrical signals, electrically switched, and then converted back to optical signals.
The traditional optoelectric approach for interconnecting optical nodes has a number of shortcomings. First, the fact that optical signals are converted to electrical signals and then back to optical signals necessarily requires components for affecting the electrical/optical conversion. These additional components tend to make the optical cross connect large and expensive. Additionally, the additional components compromise the efficiency of the overall system thereby requiring higher energy input signals and increased reliance on optical amplifiers to raise the input signals to the appropriate level. Finally, by converting between the optical and electrical domains and switching in the electrical domain, optoelectric cross-connects are slower and encounter electrical historesis which limits the speed of switching. Therefore, although used traditionally, the optoelectric approach to cross connects is faced with inherent problems.
Recently, the applicants have developed a purely optical cross-connect. This cross connect involves an 8 node by 8 node perfect shuffle described in co-pending application No. 60/188,427 filed on Mar. 10, 2000. Briefly, the 8×8 perfect shuffle optical circuit comprises a substrate upon which is laid optical fiber that interconnects each input node with each output node. Since this is an 8×8 cross-connect, each node comprises 8 individual fibers. The fibers extending from the tabs are typically terminated in a multi-fiber ferrule for connection to a multiplexer or demultiplexer or are terminated individually for interconnection with particular active or passive devices. An example of a multi-fiber ferrule is the Lightray MPX™ connector interconnect system commercially available through Tyco Electronics (Harrisburg, Pa.).
The purely optical cross-connect offers a number of advantages over an optoelectric equivalent. Specifically, because the nodes are interconnected purely in the optical domain, components used for converting optical signals to electrical and then back again are eliminated. This reduces costs, complexity and increases efficiency.
Although the optical cross-connect as described above offers significant advantages over optoelectric devices and overcomes many of their shortcomings, trends in the industry somewhat militate against its general acceptance. More specifically, there is an ever-increasing need for greater capacity, i.e., more nodes, especially as the number of channels in DWDM applications continues to increase. In addition to increased capacity, there is a need to reduce size. Therefore, there is a general trend in the industry to increase the node density within an optical cross-connect. Furthermore, despite these trends, there is no “standard” industry cross-connect. Different applications require different configurations and node capacity.
The applicants have identified a number of issues which somewhat restrict the ability of the optical circuit described above to meet current industry trends. Specifically, the current optical circuit design is essentially flat and the nodes are defined in basically two dimensions. Applicants recognize that as the number of nodes increases from 8 up through 64 and beyond, the area required to accommodate the flat fiber circuit and the complexity of the fiber layouts thereon become prohibitive. Additionally, designing and manufacturing specific optical circuits to meet particular application needs is impractical. Specifically, designing an optical circuit layout requires attention to a variety of factors including minimum bend radius, skew, plus other problems, such as minimizing fiber stacking and securing fibers to a substrate. It is impractical that specific optical circuits be designed and manufactured according to specific applications.
Therefore, a need exists for an optical cross-connect that not only accommodates many nodes in a compact package, but also affords flexibility in configuring the capacity of the cross-connect to meet a variety of different application needs. The present invention fulfills this need among others.